The present invention relates to the field of optical amplifiers and, particularly, pertains to optical amplifiers which operate in an infrared wavelength region. More specifically, this invention pertains to optical amplifiers comprising an organic luminescent free radical compound, wherein the luminescent free radical compound emits photons in an infrared wavelength region as a result of a photon absorption by the free radical compound followed by stimulated emission from an excited state of the luminescent free radical compound.
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent specifications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
As the quantity and speed of data communications over fiber optics systems rapidly increases due to the growing demand from Internet usage and other communications, optical amplifiers are of high interest to increase optical signal power to overcome signal losses from attenuation over long distances in the fiber optic transmission line as well as from insertion of optical components, such as optical switches, optical splitters, and optical combiners, into the fiber optic transmission line.
A variety of optical amplifiers are known, particularly rare earth doped optical fibers, such as, for example, described in U.S. Pat. Nos. 5,452,124 to Baker; 5,801,879 to Burton et al.; 5,936,762 to Samson et al.; 6,101,016 to Roberts et al.; 6,101,025 to Naganuma; 6,104,527 to Yang; 6,104,733 to Espindola et al.; and 6,067,187 to Onaka et al. U.S. Pat. No. 5,881,200 to Burt describes an optical amplifier containing a colloid of quantum dots in the light-guiding region of the optical fiber.
Rare earth doped optical fibers used in optical amplifiers typically are glass fibers of 10 to 30 meters in length because of the very low molar absorption extinction coefficients of the rare earth ions and are also not suitable for use in polymer optical fibers, where the polymer or plastic fibers are desirable for ease and low cost of fabrication of optical components, such as optical switches and amplifiers. It would be advantageous if optical amplifiers were available which avoided the size, complexity of fabrication, and high cost of rare earth doped optical amplifiers.
An organic free radical compound where the excited state is an excited state from the free radical ground state may have a rapid internal conversion from this excited state back to the ground state with a concomitant production of heat in a time scale of as low as 1 picosecond or less. In one example of this, an organic radical cation compound absorbs photons in the presence of a thermochromic compound, converts the absorbed photons to heat in less than 1 nanosecond, and causes a change in absorption due to heat-induced changes in the thermochromic compound, as described in PCT International Publication No. WO 98/54615, titled xe2x80x9cOptical Shutter Devicexe2x80x9d and published Dec. 3, 1998, to Carlson. The excited state of the organic free radical compound may undergo a photoreaction, such as a photo-induced electron transfer reaction, which causes changes in the absorption. This photoreaction may occur faster and with higher efficiency than internal conversion of the absorbed photons to heat or, alternatively, may have a similar or slightly lower speed and efficiency than this internal conversion to heat so that both photoreaction and heat formation processes occur, as, for example, described in U.S. Provisional Pat. Application Ser. No. 60/163,349, titled xe2x80x9cOptical Shutterxe2x80x9d and filed Nov. 3, 1999, to Carlson, the disclosure of which is fully incorporated herein by reference.
One aspect of the present invention pertains to an optical amplifier comprising an organic luminescent free radical compound in which an excited state of the free radical compound upon photon absorption includes stimulated emission in an infrared wavelength region. In one embodiment, the luminescent free radical compound is a salt of a radical cation, preferably a salt of an aminium radical cation, and most preferably, the radical cation is a tris (alkyl-substituted and/or non-substituted aminophenyl) aminium hexafluoroantimonate. In one embodiment, the luminescent free radical compound is a salt of a radical anion, preferably an anthrasemiquinone radical anion.
In one embodiment of the optical amplifier of this invention, the luminescent free radical compound is a salt of a radical cation, and the optical amplifier further comprises a salt of a radical anion. In one embodiment, the luminescent free radical compound is a salt of a radical anion, and the optical amplifier further comprises a salt of a radical cation. In one embodiment, the luminescent free radical compound comprises one or more salts of a radical cation and one or more salts of a radical anion, and the emission results from a stimulated emission from the excited states of at least one of the one or more salts of a radical cation and of at least one of the one or more salts of a radical anion. In one embodiment, the luminescent free radical compound comprises a salt of a radical cation and a radical anion.
In one embodiment of the optical amplifier of the present invention, the infrared wavelength region of the stimulated emission is from 700 to 1000 nm. In one embodiment, the infrared wavelength region of the stimulated emission is from 1000 to 2000 nm, preferably from 1400 to 1700 nm. and more preferably from 1500 to 1690 nm.
In one embodiment of the optical amplifier of this invention, the stimulated emission occurs in less than 1 nanosecond after absorption of photons by the luminescent free radical compound, preferably occurs in less than 0.1 nanoseconds, more preferably occurs in less than 0.01 nanoseconds, and most preferably occurs in less than 0.001 nanoseconds.
In one embodiment of the optical amplifier of the present invention, the excited state of the luminescent free radical compound is populated by ultraviolet laser radiation. In one embodiment, the excited state is populated by visible laser radiation, and preferably is populated by infrared laser radiation, such as 980 nm or 1350 nm laser radiation. In one embodiment, the excited state is populated by absorption of photons by a free radical moiety ground state of the luminescent free radical compound.
In one embodiment of the optical amplifier of this invention, the optical amplifier further comprises a metallized layer on at least one side of a layer comprising the luminescent free radical compound of the optical amplifier. In one embodiment, the metallized layer comprises aluminum.
As will be appreciated by one of skill in the art, features of one aspect or embodiment of the invention are also applicable to other aspects or embodiments of the invention.